Key
♦ - Each diamond represents how much Alexei likes a person. Up to five diamonds max. Less than or equal to 3 means acqaintances, anything more is a friendship.
◊ - Tells you how much Alexei dislikes a character. The more empty diamonds there are, the more he hates the character. They can have up to five empty diamonds max. If you see a crossbone (☠) instead, that's basically five empty diamonds and it's going to be difficult to change his opinion of the character at this point.
★ - Each star represent how much Alexei is willing to trust a character. A character can have up to three of these. One means he will say more than just formalities, like having longer conversations with them and three means he is willing to confide the character with more personal matters. Two is somewhere in-between that.
♥ - Self-explanatory. If there's a heart, then Alexei has grown an attachment for that character or is a romantic interest.
■□□□□□□□□□ - This bar basically shows how much Alexei knows a character. Full bar means he knows enough of the character to skip most formalities.